Burning device for burning ore pellets and similar bodies

ABSTRACT

A burning device with a movable grid system for supporting a bed of ore pellets or the like for burning (baking) them, comprising in sequence one behind the other at least one drying zone, one burning zone and two cooling zones, and in which means are present for supplying water in the second cooling zone, characterized in that the first cooling zone at the discharge side of the cooling fluid, above the movable grid system, is connected by passages to the burning zone and the drying zone, and that the second cooling zone is passed in downward direction by the cooling fluid with the aid of a suction fan which is connected to a flue gas stack of the burning machine. This gives more efficient cooling, more uniform temperatures in the ore pellet bed and the least possible corrosion difficulties.

States tet [1 1 iewinga Mar. 18, 1975 [75] Inventor: Siewert Gerrit Jan lBiewinga,

Velsen, Netherlands [73] Assignee: Hoogovensljmuiden B.V., Ijmuiden,

Netherlands [22] Filed: Nov. 21, 1972 [2]] Appl. No.: 308,559

[30] Foreign Application Priority Data Nov. 24, 1971 Germany...... 2158317 [52] U.S. Cl. 266/21, 266/20 [51] Int. Cl. F27b 21/00 [58] Field of Search 266/15, 16, 20, 21; 75/3, 75/5 [56] References Cited UNITED STATES PATENTS 1,083,252 12/1913 Hall 266/21 X 1,181,244 5/1916 Payne 266/21 X 2,252,714 8/1941 Hall 266/20 X 2,498,766 2/1950 Pettigrew 75/5 2,672,412 3/1954 Burrow et al.. 266/21 X 2,851,042 9/1958 Spence 266/6 S 3,005,699 10/1961 Erck et a1. 266/21 X 3,244,507 4/1966 Linney 266/21 X OTHER PUBLICATIONS from Blast Furnace and Steel Plant, pp. 745-752, July, 1955.

A. English & M. F. Morgan, Downdraft Taconite Pellet Hardening, from Journal of Metals, pp. 122-124, February, 1958.

Primary Examiner-Roy Lake Assistant Examiner-Paul A. Bell Attorney, Agent, or Firm-Hall & Houghton [57] ABSTRACT A burning device with a movable grid system for supporting a bed of ore pellets or the like for burning (baking) them, comprising in sequence one behind the other at least one drying zone, one burning zone and two cooling zones, and in which means are present for supplying water in the second cooling zone, characterized in that the first cooling zone at the discharge side of the cooling fluid, above the movable grid system, is connected by passages to the burning zone and the drying zone, and that the second cooling zone is passed in downward direction by the cooling fluid with the aid of a suction fan which is connected to a flue gas stack of the burning machine. This gives more efficient cooling, more uniform temperatures in the ore pellet bed and the least possible corrosion difficulties.

4 Claims, 3 Drawing Figures BURNING DEVICE FOR BURNING ORE PELLETS AND SIMILAR BODIES This invention relates to a burning device with movable grid connected to a chain system to burn ore pellets or the like, which device comprises in series at least one drying zone, one burning zone and two cooling zones, and means for supplying water in the second cooling zone.

In previously known burning (baking) devices of this type air was made to move upwardly through the cooling zone, the cooling air discharged from the first cooling zone being used as air for combustion in the burning zone and as drying fluid in part of the drying zone. Cooling water was supplied to the second cooling zone from above so that the cooling air moving upwardly in this zone was mixed with water vapour or steam. In many cases this mixture was then fed to another part of the drying zone to pre-dry the material to be burned. For blowing the cooling air through the two cooling zones a single fan was used.

It has appeared that such a burning device can be im proved considerably. It is an object of this invention first of all to shorten the necessary length of the cooling zone and to improve the cooling. In trying to obtain this it has appeared that there are several factors making such a shortening very difficult.

As in said known plants the cooling air is fed over the entire length of the cooling zones from below to above through the bed of material to be cooled, there remains a temperature gradient over the total length of these zones in the material to be cooled. If the requirement is made to this material that, when leaving the cooling zone, it should have a certain temperature, a considerable part of. this material will be very much colder than this required temperature and this is not necessary and not desired.

Another disadvantage is experienced when supplying cooling water in the second cooling zone. This is so because it has appeared that a considerable part of this water vaporizes already in the upwardly flowing air stream or in a thin upper layer of the material to be cooled. Thereby this cooling water is not very effective in its cooling function, but nevertheless it raises the dew point of the mixture of air and water vapour in a disadvantageous way. This gives restrictions to the use of this mixture as drying fluid in the drying zones. Thus it is according to the invention aimed at to obtain a more effective cooling with a smaller quantity of water. It is remarked in this respect that in the present situa tion of existing burning machines it is not well possible to spray water in the same main direction as the flow of cooling air onto the lower surface of the moving grid structure. This is so because this water will in part not at all reach the material to be cooled and moreover there will be much wear in the moving grid structure by corrosion.

In view of the above the invention consists in that in the known burning machine as indicated above the first cooling zone is at the discharge side, above the moving grid, connected by passages to the burning zone and the drying zone, and that the second cooling zone is passed by the cooling fluid in a downward direction with the aid of a suction fan connected to a flue gas stack of the burning machine. In this embodiment the bed with the material to be cooled will be cooled in the cooling zones from different sides, so that the temperature distribution in this material after cooling will be more uniform. If cooling takes place to a same maximum temperature of the material, the average temperature of this material can thereby become higher, which entrains the possibility to shorten the cooling zones. Moreover, this warrants that all cooling water supply is indeed effective in cooling the material, as this water, as water vapour or steam, is entirely sucked through the bed with the material to be cooled.

Thus, in the drying zone there is nowhere used a gas mixture with a high content of water vapour or steam as the drying fluid. Thus the danger of condensation of water in these drying zones is entirely avoided.

It is remarked that in the new proposal for the burning machine all heat which is transmitted to the cooling fluid in the second cooling zone is lost because this part of the cooling fluid is entirely discharged to the stack. Moreover, it is now necessary to use an additional suction fan for'serving the second cooling zone. It has, however, appeared that these disadvantages are not of much importance. This is so because it has appeared that the lower capital investment costs by the possible shortening of the cooling zones make up amply for the additional investment in a suction fan. The said additional stack losses are neither serious. This is so because it is quite well possible to adapt the quantity of cooling air through the first cooling zone to the need of drying fluid in the drying zone and combustion air in the burning zone and thus it is possible, with the new method according to the invention, to maintain the losses through the stack at the same level as in the known method as indicated above. As the drying fluid in the drying zones is free from water it is moreover possible to operate the burning machine in a more simple manner. It has not only appeared important that by the more uniform temperature distribution in the cooled product the average temperature of this product may be allowed to reach a higher value, but moreover it has appeared that for the further processing of the ore pellets thus burned and cooled it is important that the temperature thereof after cooling is more uniform. In particular this advantage plays a role with respect to the dust generation in the ore pellets after manufacture.

In former proposals to meter water into the second cooling zone this metering should preferably take place at the entrance side of the second cooling zone. This is based upon the idea that metering of water onto the ore pellets still warm, close to the end of the second cooling zone, could give rise to formation of steam from the ore pellet bed when leaving the cooling zones. This formation of steam could also give rise to the conveying of dust from the ore pellets into the factory hall. It has, however, now appeared that in the method of cooling as proposed according to the invention there is almost no steam and dust issuing from cooled ore pellets when leaving the cooling zone. This is even so if a disperature which is too high to make a direct water cooling desirable. Thus the beginning of the water cooling should preferably be chosen in a zone where the hottest ore pellets have been cooled down to a temperature of 300 350C. If optimum cooling results are desired, the water cooling should neither begin in a zone where the temperature of the ore pellets is much lower, and it is neither effective to make the water cooling so intense that the temperature of the hottest ore pellets will finally drop below 100C. In order to be able to realize the most optimum conditions at all times it is according to the invention preferred that the distributing system as to quantity and distribution of the water is made adjustable. This adjustability appears to be quite suited for automation if according to the invention the adjustable distributing system is governed by control means depending on the temperature of the burned material at the beginning and the end of the cooling water distributing system. As this temperature at the beginning is higher, the point where the water cooling begins should be displaced more backwardly, and as the said final temperature is higher, the total quantity of cooling water should be increased.

As has already been remarked, the stack losses of the burning machine can be restricted to a minimum if the quantity of cooling air passing through the first cooling zone is adapted to the required quantity of combustion air in the burning zone and to the desired drying capacity of this heated cooling air in the drying zone. As a result of variations in the quality of the product to be burned and in the way of operation of the burning machine the real situation may deviate from the nominal situation for which the plant has been designed. In order to be able to make small adaptations and corrections in the way of guiding the process it is according to the invention preferred to apply a fan in the connecting passage from the first cooling zone to the drying zone, and to connect an inlet passage and an outlet passage onto this connecting passage from the first cooling zone to the drying zone, and to connect an inlet passage and an outlet passage onto this connecting passage to both sides of said fan, each of said inlet-and outlet passages having an adjustable passage area. It is, e.g., possible for the inlet duct to suck additional cold air from the environment if the desired quantity of drying fluid is too low in volume or it too hot. The exhaust passage may be connected to the flue gas stack and may be used to discharge a surplus of hot air if the quantity of drying medium is too high.

The invention will now be explained in more detail with reference to the enclosed drawings. In said drawmgs:

FIG. 1 shows diagrammatically a possible and pre ferred embodiment of the burning machine according to the invention.

FIG. 2 shows a detail from FIG. 1 on an enlarged scale.

FIG. 3 shows the course of temperature through an ore pellet bed.

In FIG. 1 reference numeral 1 shows a chain structure composed of grid cars, conveyed over two sprocket wheels 2 and 3 and moving in the direction of the arrow. This chain therewith passes in subsequence through a first drying zone 4, a second drying zone 5, a burning zone 6, a first cooling zone 7 and a second cooling zone 8. In this FIG. hoods are shown around the cooling zones for guiding gaseous fluids to and from the grid structure. Several fans are applied for displacing these gaseous fluids, such as a blowing fan 10 for the supply of air to cooling zone 7 and a suction fan 11 for sucking away cooling air from cooling zone 8 through duct 18 to pump it to stack 9, and a system of boosting fans 12 for sucking away combustion gases from the burning zone 6 and for the displacing thereof to the drying zone 4, a suction fan 13 for sucking away these combustion gases from drying zone 4 to stack 9, a boosting fan 14 for sucking heated cooling air from cooling zone 7 and displacing this air through passage 19 to the second drying zone 5, and exhaust fan 15 for sucking away the drying air which has passed the drying zone 5, and, if desired, for also sucking combustion gases from part of the burning zone 6 (not shown).

In FIG. 1 a number of burners 16 is shown which maintain within the burning zone 6 a gas temperature of about 1,320C. In the cooling zone 8 water spray nozzles 17 are provided, adapted to spray water onto the burned mass over the entire length of this zone. It is clear from FIG. 1 that the cooling fluid in cooling zones 7 and 8 is guided in opposite directions through the layer of burned ore pellets. Moreover, in cooling zone 8 the water sprayed onto the layer and the vapour or steam therefrom is sucked through the layer of material to be cooled. In this plant as shown in FIG. 1 the several zones have lengths which have the following values in proportion to the length of the burning zone 6 percent):

first drying zone 4: 32 percent second drying zone 5: 35 percent first cooling zone 7: 58 percent second cooling zone 8: 27 percent.

These ratios are of course only by way of example as they are as such depending on other factors such as the distribution of pressures through the entire plant.

In the second drying zone 5 there are also burners of the same type as in the burning zone 6, which if necessary can serve to increase further the temperature of the drying fluid.

As a branch from passage 19 there is an exhaust duct 20 provided with a control valve 21. This exhaust duct 20 is connected to the stack 9. With the aid of control valve 21 it is possible to decrease the quantity of drying fluid. There is also an inlet duct 22 with a control valve 23, connected at the inlet side of the fan 14 and serving to increase the quantity of drying fluid for drying zone 5 if necessary and/or to decrease the temperature thereof.

In FIG. 2 the second cooling zone 8 is shown on an enlarged scale, but also diagrammatically.

On the moving grid system 1 the burned mass of ore pellets moves in the direction of the arrow. Within a hood 25 a number of water spray nozzles 17 is provided, fed from a central water supply, but each connected to this central water supply 26 through supply ducts 27. In each of the supply ducts 27 there is a control valve 28. In this drawing five nozzles 17 have been shown, but it will be clear that this number may be altered at will. Each control valve 28 is connected through an energizing line 29 to a control device 30, adapted to move each one of the valves 28 independently into each position between full open and full closed.

Governor R controls the position of the valves 28 in such a way that water is first sprayed in a zone where the temperature of the ore pellets has a certain desired value, the total quantity of water being adjusted by the control device 30 depending upon a second desired temperature of the ore pellets at the end of the cooling zone 8. To this end the control device 30 receives signals from temperature sensors 31 and 32 positioned in the zone where in normal operation water is first sprayed onto the pellets and at the end of the coding zone 8 respectively.

In FIG. 3 several curves have been shown for explanining the effect of the invention. Along the vertical axis the thickness of the ore pellet bed on the belt system 1 is indicated, and horizontally the temperature of the ore pellets is given. Four lines have been given in PK]. 3. Line a gives the temperature course in the ore pellet bed where belt 1 enters the cooling zone 8. It appears therefrom that the lower ore pellets have taken up about the temperature of the cold cooling air, whereas the upper ore pellets in the bed still have a temperature of about 550C. Line b gives the temperature course over the height of the bed in the zone of the end of the cooling zone 8 if only fan 11 sucks cooling air from top to bottom through the layer without any water being sprayed. It will be clear that the course of this temperature is to a considerable extent depending on the quantity of cooling air sucked through the layer, but this line only gives one typical operating condition. It appears from this drawing that the upper ore pellets now have taken up the temperature of the environment, but that the heat present in the bed is conveyed downwardly. Here the lower ore pellets are clearly too hot. However, it appears from the course of line b that the temperature difference between the hottest ore pellets and the average temperature of the bed has de-' creased considerably. Line 0 shows the temperature course of the ore pellets at the end of the cooling zone 8 particularly when water has been sprayed onto the bed by means of the spray nozzles 17. The quantity of water has here been chosen so that the hottest ore pellets have a temperature of about 90C. For comparison with this cooling result line d has been shown. This line gives the temperature distribution in the ore pellet bed at the end of the cooling zone 8 in a case in which the invention is not applied. Thus, in this case, according to the known method, cooling air is blown vertically upwards through the second cooling zone, the same quantity of cooling air and the same quantity of water being metered to the layer as in the case of line 0. When comparing curves c and d it appears clearly that in case of the known method of line d a rather considerable percentage of the ore pellets still has a temperature of much higher than 100C. These ore pellets will thus, after leaving the cooling zone, become entirely dry so as to give dust problems. As curve c has a convex shape instead of a concave shape as curve d, the temperature of the hottest ore pellets is lowered to below 100C, so that these ore pellets can better be moistened and kept moist a little.

What I claim is:

l. A burner device for the baking of ore pellets and the like comprising in sequence, one after the other, at least one drying zone, a burning zone, a first cooling zone, a second cooling zone, a movable grid system for supporting a bed of ore pellets to be baked passing through each of said zones in a longitudinal path, said first cooling zone being connected at one end to said burning zone and drying zone by a passageway extending over said movable grid system, the opposite end of said first cooling zone having means to draw cooling air thereinto for passage upwardly through said movable grid system, said second cooling zone having water distributing means at its upper end thereof for supplying cooling water for passage downwardly through said movable grid system, the opposite end of said second cooling zone having means for carrying off said cooling water after passage through the grid system, said water distributing means being positioned above said movable grid system from a point at a distance of about 15 to 30 percent of the length of said second cooling zone from the entrance end thereof up to close to the exit end thereof.

2. A burner device in accordance with claim 1, wherein the water distributing means is adjustable as to the quantity and the distribution of water.

3. A burner device in accordance with claim 2, wherein said water distributing means includes control means operable in relationship to the temperature of the burned ore pellets in the zone at the beginning and at the end of the water distributing means.

4. A burner device in accordance with claim 1, wherein the passageway connecting the first cooling zone to the drying zone includes fan means, said fan means including an inlet duct and an outlet duct connected to said passageway with each duct having an independently adjustable passage area for the controlled supplying and discharging respectively of air from the atmosphere to or from the system. k 

1. A burner device for the baking of ore pellets and the like comprising in sequence, one after the other, at least one drying zone, a burning zone, a first cooling zone, a second cooling zone, a movable grid system for supporting a bed of ore pellets to be baked passing through each of said zones in a longitudinal path, said first cooling zone being connected at one end to said burning zone and drying zone by a passageway extending over said movable grid system, the opposite end of said first cooling zone having means to draw cooling air thereinto for passage upwardly through said movable grid system, said second cooling zone having water distributing means at its upper end thereof for supplying cooling water for passage downwardly through said movable grid system, the opposite end of said second cooling zone having means for carrying off said cooling water after passage through the grid system, said water distributing means being positioned above said movable grid system from a point at a distance of about 15 to 30 percent of the length of said second cooling zone from the entrance end thereof up to close to the exit end thereof.
 2. A burner device in accordance with claim 1, wHerein the water distributing means is adjustable as to the quantity and the distribution of water.
 3. A burner device in accordance with claim 2, wherein said water distributing means includes control means operable in relationship to the temperature of the burned ore pellets in the zone at the beginning and at the end of the water distributing means.
 4. A burner device in accordance with claim 1, wherein the passageway connecting the first cooling zone to the drying zone includes fan means, said fan means including an inlet duct and an outlet duct connected to said passageway with each duct having an independently adjustable passage area for the controlled supplying and discharging respectively of air from the atmosphere to or from the system. 